The objective of the proposed research is to study the interactions or symbiotic relationships involving members of the normal, indigenous microflora and the human body. Spirochetes, which inhabit several regions of the healthy human body, will be used as a tool or model to gain information on the physiological, ecological, and ultrastructural factors involved in associations or symbioses between humans and indigenous microorganisms. We intend to study the physiological interactions between the human body and spirochetes which are normal inhabitants of the gingival crevice and interproximal areas of teeth, of the intestinal mucosa, and of the external genitalia. The interrelationships between these spirochetes and the indigenous microflora sharing the same habitats will be investigated. These studies are expected to contribute to the understanding of infectious processes in which the indigenous microflora participates, and to help clarify aspects of the close association between the human body and pathogenic spirochetes. BIBLIOGRAPHIC REFERENCES: E. P. Greenberg and E. Canale-Parola. 1975. Carotenoid pigments of facultatively anaerobic spirochetes. J. Bacteriol. 123, 1006-1012. J. A. Breznak and E. Canale-Parola. 1975. Morphology and physiology of Spirochaeta aurantia strains isolated from aquatic habitats. Arch. Microbiol. 105, 1-12.